Method and Installation for Unsupported Lean Fuel Gas Combustion, Using a Burner and Related Burner

ABSTRACT

The invention concerns a method for a lean gas combustion using at least one burner including a combustion nozzle on a central axis (x). The method includes creating a mixture of fuel gas and combustion air rotating about the central axis, and ejecting a flow of non-flammable premix containing a mixture of premix air and fuel gas in front of the combustion nozzle. A complementary flow achieves a non-flammability threshold of the mixture in front of the combustion nozzle, the flow being ejected at the center of the premix flow via a central complementary flow and/or about the premix flow via a peripheral complementary flow. The invention also concerns a burner configured to implement the method and a combustion installation using same.

CROSS-REFERENCE TO RELATED U.S. APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

NAMES OF PARTIES TO A JOINT RESEARCH AGREEMENT

Not applicable.

REFERENCE TO AN APPENDIX SUBMITTED ON COMPACT DISC

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention concerns a method for achieving combustion of anunsupported lean fuel gas, using a burner including a gas port nose on acentral axis, creating, inside the burner, a mixture of fuel gas andcombustion air, rotating around the central axis and in front of the gasport nose.

It also concerns a burner structure, particularly of great strength, forthe application of the method and any gas combustion installation usingthis burner.

The invention is applied particularly in the various followinginstallations:

-   -   Heating boilers, using gas of very low calorific value, waste        gas (blast furnace gas . . . ), biogas and relief gas and gas        originating from various processes;    -   Burn-off towers and flares of lean, residual gases and biogas;    -   Furnaces and drying ovens for various materials and products;    -   Furnaces and devices for drying and treatment of residual sludge        generated by various processes; and    -   Installations for burning volatile organic compounds “VOCs”.        These VOC compounds originate from drying or baking in different        processes. Often these are fumes of solvents or oils and are        found in very weak concentration (a few % at a few ppm or        traces) in neutral carrier gases or in air. They may be blocked        by dedicated filters or destroyed by thermal means. The low        concentration does not allow burning them off directly and the        large volume of air containing them significantly disturbs the        combustion of the “classic” burners.

By lean gas, it is meant any gas of low calorific value, i.e. less than3000 Kcal/m³ and in particular any very lean gas with a net calorificvalue (NCV) below 1000 Kcal and which concerns more specifically thesubject of this invention.

The burner in accordance with the invention may nevertheless be usedwith richer gases or with support gases.

2. Description of Related Art Including Information Disclosed Under 37CFR 1.97 and 37 CFR 1.98

The burners of lean or residual gases include generally various infeedpipes of combustible fluids to the burner nozzle, the pipes beingconfigured, especially in a coaxial shape, so as to create one or morerings of combustibles centered on the axis of the burner.

These combustible fluids are generally distributed in a flux ofcombustion air or on the periphery of the latter.

The above dispositions have the ultimate goal of creating an adequateair/fuel mix for achieving localized and stabilized combustion at thenose of the burner.

On high capacity boilers (>100 MW) which include several burners (>4burners), the combustion air is usually distributed from a common airbox to all burners and put into rotation by flaps that are adjustablefrom the outside by gear mechanisms and link rods.

This combustion air is generally fed to the nose of the burner(hereafter called combustion burner) in one flux or even in two.

These burners usually include rich gas distribution tubes in aperipheral ring and accessory tubes (ignition burner, flame presencecontrol tube, . . . ) which upset the rotation of the air flux.

The majority of lean or residual gas burners is of a complex design andrequire unplanned settings and adjustments as well as very rigidoperating conditions with a considerable number of incidents due to theinstability of the combustion, of the flame catching on, leading toill-timed shut-down events of the installation.

These burners require reheating of the fuel and especially of thecombustion air at high temperatures (250 to 350° C.) [480 to 660° F.] inorder to improve combustion which involves more items of appropriateequipment and additional costs.

Lean combustibles are generally very difficult to burn because theyconsist primarily of neutral gases and present themselves distributed inlarge volumes and under low pressure.

Mixing them with combustion air in adequate proportions is a verydifficult undertaking, considering the volumes involved which isseriously hindering combustion and does not favor the stability andstructure of the flames obtained.

The instability of the flames produced causes major variations ofpressure in the combustion chamber, thereby generating vibrations of thestructure of the boilers or installations concerned.

For this reason the burners always require a support flame, representing10 to 20% of the total capacity of the burner, to ensure stability ofthe main flame and to guarantee the safety of the installation.Operating norms EN 746-2 make support flame systems mandatory in theburners.

These support flames are obtained with rich gases (natural gas,Liquefied Petroleum Gas (LPG)): Butane and Propane.

This requirement increases the complexity of the burner and inevitablycauses very substantial extra expenditures, considering the price ofrich gases.

The burners often require to be operated with a substantial amount ofexcess air to make sure that all combustible fractions are exposed tooxygen for a complete burn and in order to ensure the quality of thecombustion products, which causes profits to shrink considerably,increases the specific consumption of rich gas and hence the operatingcosts and inevitably raises the level of polluting emissions.

The invention aims to remedy the above drawbacks.

It offers in particular a burner design which allows:

-   -   as much as possible to do without a rich gas support;    -   to do without reheating of the gas or the combustion air;    -   to reduce the oxygen content of smoke;    -   to eliminate vibrations; and    -   to reduce the consumption of electric power of air and smoke        ventilators.

A preferred basic principle of the method is to partition as much aspossible the quantity of air needed for combustion and to incorporate itas soon and as intimately as possible into the combustible gaseous flux(or the inverse), by improving the mixture through high-speed jetimpacts by creating incidents of turbulence and by putting the mixtureinto maximum rotation in order to reduce the axial velocity of themixture and to ensure the consistency and continuity of the combustion.

To reduce the axial velocity and to increase the flame surface, the leangas is put into rotation by blades and the specific flow of the fractionof combustion air brought in at the periphery at the exit of the burner.

Since lean gases do not have a large volume, it is difficult tointimately mix the combustible elements of this gas with the oxygen ofthe combustion air. To lessen this less difficulty the inventionconsists of fragmenting the combustion air and of progressivelyincorporating chosen quantities of it into the lean gas flux.

The method consists therefore of creating a pre-mix of air and fuel(outside the flammability limit) preferably inside the body of theburner and to bring to the nose of the burner only the air complement onboth sides of this mixture through the expedient of jets at very highspeed (above 80 m/s) [above 262.5 ft/sec] by making the gas “in asandwich”.

The combustion air directed to the nose of the burner has specific flowsat high speed:

-   -   the central air is ejected in rotation and in divergent flow in        order to penetrate the lean gas; and    -   the peripheral air is convergent and in strong rotation.

These two air flows also both have the function to form a barrier topotential “flashbacks” at a low intensity or during a shutdown of theinstallation.

BRIEF SUMMARY OF THE INVENTION

To that effect, the subject of the invention is a method to obtain thecombustion of a lean fuel gas using at least one burner including a gasport nose or head on a central axis, a process in which a mixture offuel gas and combustion air is created in rotation around a centralaxis.

The method distinguishes itself by consisting of the following stages inwhich the following are ejected in front of the combustion head:

-   -   a flux of nonflammable pre-mix containing a mixture of pre-mix        air and of fuel gas; and    -   a complementary flux so as to reach an ignitibility threshold of        the mixture in front of the gas port nose, the flux being        ejected in the middle of the pre-mix flux by way of a        complementary central flux and/or around the pre-mix flux by way        of a complementary peripheral flux.

According to particular application modes of the method:

-   -   the complementary flux is an air flux;    -   the pre-mix flux is obtained through incorporation of pre-mix        air into fuel gas;    -   the incorporation is achieved in a mixing chamber connected to        the burner;    -   the incorporation is made, at an entry of the fuel gas into the        burner by injection of pre-mix air into the fuel gas in a manner        such as to draw the fuel gas in a pre-mix space, to obtain the        pre-mix through incidents of turbulence resulting from the        injection and to direct the pre-mix towards the gas port nose by        initiating a rotation around the central axis; and    -   the mixture of fuel gas and combustion air is obtained by        incorporating a necessary partitioned quantity of one in the        other by numerous directed jets.

According to another mode of applying the method:

-   -   a) the flux of central complementary air is ejected in rotation        in front of the gas port nose and in divergent discharge to        penetrate the pre-mix flux; and    -   b) the flux of peripheral complementary air is ejected in        convergent discharge and in a strong spiral rotation.

The invention is also concerned with a burner for lean fuel gas of thetype that includes a gas port nose on a central axis and means to feed amixture of fuel gas and combustion air in rotation around the centralaxis, the burner being especially noteworthy because it includes neithera mixing chamber nor a combustion chamber.

The burner distinguishes itself primarily by being configured so as toeject in front of the gas port nose:

-   -   a nonflammable pre-mix flux containing a mixture of pre-mix air        and fuel gas, and    -   a complementary flux so as to reach an ignitibility threshold of        the mixture in front of the gas port nose, said flux being        ejected to the center of the pre-mix flux by way of a flux of        central complementary air and/or around the pre-mix flux by way        of a flux of peripheral complementary air.

According to a particular way of carrying out the invention, the burneris configured so as to divide a flux of air into at least one flux ofpre-mix air and a flux of complementary air, comprising at least oneflux of central complementary air and/or one flux of peripheralcomplementary air.

The invention is also concerned with an installation for the combustionof fuel gas applying the method or comprising at least one burner inconformance with the invention.

According to an advantageous characteristic, the installation uses orincludes at least two burners that are configured so as to gear in acommon direction the overall rotary motion resulting from their mixtureflux in front of the gas port nose.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Other particularities and numerous advantages of the invention willappear in the description below, given as an illustrative andnon-limiting example, and made with reference to the attached figures.

FIG. 1 shows a schematic view of an installation for lean gascombustion, equipped with a burner in accordance with one way ofcarrying out the invention.

FIG. 2 shows a partial sectional view along axis AA of FIG. 1.

FIG. 3 shows a back view of the burner as per the right side view ofFIG. 1.

FIG. 4 shows a partial sectional view of a beam as per section CC ofFIG. 2.

FIG. 5 shows a partial bottom view as per D-D of FIG. 4.

FIG. 6 shows a detailed schematic view of the chamber 7 of the burner inFIG. 1.

FIGS. 7, 8, and 9 show different sectional and partial section views,respectively, of FIG. 6: a sectional view along E-E, a right side viewalong F, and a left side view along G.

FIGS. 10, 11, and 11A show, respectively, a detailed schematic view ofthe central tube 13 of the burner of FIG. 1, a left side view along Hand a right side view.

FIG. 12 shows a detailed sectional view of the central pole 50 as perFIG. 1.

FIG. 13 shows a partial sectional and schematic view of a constructionvariant of a flaring cone of the central pole.

FIG. 14 shows a detailed sectional view of FIG. 9.

FIGS. 15 and 16 show, respectively, the sectional views along L-L andK-K of FIG. 14, respectively.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an installation 1 for the combustion of lean fuel gas,using a burner 2 mounted between 4 main parts ZA, Zb, ZC, ZD that areseparated by three partitions 3,4,5.

The parts represent, respectively, a zone ZA firebox where combustiontakes place, a zone ZB containing or in communication with the lean fuelgas, a zone ZC containing or in communication with combustion air, azone ZD that is exterior to the installation and accessible topersonnel.

The installation is, for example, a production facility for superheatedsteam at a rate of 40 T/hour in which blast furnace gas is to be burnt,at ambient temperature, (humidity=2.5% of H₂O by volume), low-pressurefed (<300 mm CE relative pressure) and an average composition on drygas: N2=58%, H₂=1.7%, CO₂=20.3%, CO=20% (PCI=660 Kcal/m³n). The productsof combustion must contain less than 50 ppm of CO with less than 1% ofoxygen in these fumes. Ignitibility of this gas occurs when there is 35%to 73% of gas in the mixture.

The burner includes a gas port nose 6 ending in Zone A of the chamber.The nose is centered on a central axis X which happens to be, under thecircumstances, the main axis of the burner to the extent that the latterhas a general circular shape around this axis.

The burner also includes means to feed this nose which are capable ofejecting a flux of air and fuel gas in rotation around a central axiscentered on the gas port nose.

This nose which constitutes the front end of the burner is intended toreceive, in front of or on it, to the left of the figure, a flux of fuelgas and combustion air which is put into rotation around the centralaxis, with means to feed this nose provided for this purpose and whichare described subsequently.

The burner also comprises a central chamber 7 connected to the nose andupstream of the burner (relative to the direction of the flux discharge)and mounted in zone ZB between partitions 3 and 4, with at least oneopening 8 ending in this zone ZB.

In zone ZC, there is a back end 7B of the burner linked to chamber 7,upstream of the latter, and presenting at least one access for at leastone inflow of combustion air of zone ZC.

The air supply in the preferred example is done entirely by the rearface of the burner for several advantages:

-   -   guarantee the tightness of the assembly;    -   facilitate access to the pre-mix air controls;    -   be able to install the burner in the air chamber; and    -   be able, depending on the application, to realize separate        supplies of different types of combustion air.

In zone ZD, various pipes discharge which extend between the chamber andthe exterior, while crossing the burner and among which pipes one finds,if applicable, a rich gas supply pipe, a flame control pipe, an ignitionpipe or other pipes or equipment known to the experts (not shown).

According to a way of carrying out the invention, the method may includea first stage in which a flux of air intended for combustion is dividedinto at least one flux of ore-mix air and a flux of complementary air.The complementary air is constituted of at least one central flux of airand/or one flux of peripheral air.

In the example shown, one uses both the central and the peripheral fluxof air for improved efficiency and versatility in usage and the divisionis made by different air inlets at the back of the burner or routing ofthe air in the burner.

To this effect, in the example of execution shown, the burner isconfigured to divide the air coming from the space ZC into several flux(flows). It comprises a number of intakes or access on its back end: acentral access 9 to receive an intake of a flux of central air, aperipheral access 10 to receive an intake of peripheral air, and atleast one main access 10A to receive an intake of pre-mix air. Moreaccess points can be added as indicated later on.

In a variant execution, this dividing step could be done differently,for example by external pipes outside the burner, and each flux of aircould be supplied by independent and external pipes.

In a second step of this type of execution, in front of the gas portnose, a pre-mix flux is ejected containing a mixture of pre-mix air andof fuel gas, in rotation around the central axis. The pre-mix flux isnonflammable to the extent that it is mixed at a rate far from theignitibility ranges, for example above an ignitibility threshold. Ineffect, in the example described here, one goes from a lean gas rate of100% to a rate of 80-85% (in the gas+air mixture) whereas the limits ofignitibility are between 30 and 73% in the mixture.

This assumes that the pre-mixture and its rotation are carried outbeforehand, as described below.

In order to improve combustion and to ensure good flame retention, it isof interest and importance to achieve the most thorough pre-mixture andat the earliest moment possible.

For this second step, the burner, in the example described, isconfigured to achieve the preceding pre-mix inside itself, in thisparticular case in a so-called pre-mix space 16 of the chamber 7.

It is also configured to place the pre-mix into rotation. This rotation,in the example described, is also preferably achieved in the chamberupstream of the gas port nose.

To this effect, the pre-mix air access points 10A mentioned above leadto the chamber for the same reason as the fuel gas access ports 8 forthe purpose of obtaining a pre-mixture using the mixing devices 11described later on.

However, in a variant, the pre-mixing could be done beforehand outsidethe burner, for example, in an enclosure provided for this purpose inwhich a rate above the ignitibility rate is maintained.

For the gas concerned of the example, the mixing occurs at a ratebetween 5 and 20% above the ignitibility threshold with an insufficientair percentage (proportions going between 78 and 95% gas in themixture),

For reasons of safety and efficiency, one prefers to adopt a rate thatis 10 to 20% below the total air to be supplied.

As a variant, one could, for certain applications, implement the methodby obtaining a pre-mixture with an insufficient rate of fuel gas in thesame proportions between 5 and 20% or with different proportions forparticular applications of biogas or VOC (volatile organic compounds)burns.

In a third step of execution, the complementary flux is ejected a thecenter of the pre-mix flux by way of the flux of central complementaryair and/or around the pre-mix flux by way of the flux of peripheralcomplementary air, in a manner so as it reaches the threshold ofignitibility at the gas port nose.

In the example described, ejection of the complementary flux occurssimultaneously at the center and in the periphery in order to achieve abetter final mix.

For this purpose, the burner is configured so as to deliver thepre-mixture flux in the form of ring 12 located between a central pipe13 and the periphery 14 of the front end of the chamber.

According to a mode of execution of the method, the pre-mixture flux isobtained by incorporating pre-mixture gas in fuel gas.

In effect the lean, and generally residual, combustibles are distributedunder very low pressure and in consideration of the large volumesinvolved, it is important to facilitate the flow of these gases by theeffects of mechanical drives.

For this application, the burner includes the incorporating devices 11mentioned earlier which inject air into the fuel gas.

Incorporation is done directly in an enclosure of the chamber having apre-mixture space 16 (FIG. 2) located between a central pipe 13 and aninternal partition 31 of the chamber.

According to a mode of execution, incorporation is achieved by injectionof pre-mix air at an entry point of the fuel gas into the burner so asto:

-   -   drive the fuel gas into a pre-mix space 16,    -   obtain the pre-mixture by turbulence resulting from the        injection, and    -   direct the pre-mixture towards the gas port nose while        initiating a rotation around the central axis.

For this purpose, the burner includes injection devices includingnozzles 17 or calibrated directional high-output orifices located in theincorporation devices 11 that are profiled and directed towards thepre-mixture space 16 at the ports 8.

The gas located near and around the ports 8 is driven by the partialvacuum generated by the air jets at the exits of the nozzles which aredirected by the orientation of the jets and [the gas] is mixed by theturbulence created by the jets. A rotational movement of the mixture isalso initiated in the pre-mixing space by the orientation of the airjets.

These injection devices are preferably for constant duty.

The incorporating devices may also preferably comprise second means ofpre-mix air injection. These means of injection are placed so as toobtain an incorporation of air parallel to the central axis and bydirecting the pre-mix flux towards the gas port nose.

These means of injection have preferably a progressive state conditiondepending on the level of power used.

These second means of injection may be formed, as in the exampledescribed, by tubes 21 around orifices 22 in the partition 23 of theback end of the burner (FIGS. 3, 10, 11). These tubes are preferably ofdifferent lengths and are five in number in the example. They extend tothe interior of the pre-mixing space from air intakes or orifices 22located on the partition 23 or back face of the burner.

The orifices 22 are preferably capped by flaps (not shown) that can beoperated by scaled springs or electric controls.

The flaps may be located on the orifices with or without tubes. Thetubes allow, on the one hand, to avoid the respective flows upsettingeach other and, on the other hand, to supply air at different pointswith a guarantee of its distribution.

The orifices have a determined size so as to avoid finding themselvestoo massively inside the limits of ignitibility and that there maylocally be conditions that are favorable to a combustion that woulddeteriorate the burner.

Alternatively, one could obtain the incorporation of gas in the air, forexample by interchanging the different inflows and regulating therespective outflows. This variant may be considered in particular forheating large volumes of air (drying applications) or for burning VOCs.

In this case, the pre-mixture gas would replace the pre-mixture air andthe flows, the pre-mixture could be unchanged and the central andperipheral flows could involve for instance fuel gas instead ofcombustion air.

According to one way of carrying out the invention, the flux of centralcomplementary air is ejected in rotation in front of the gas port noseand in divergent flow to penetrate the pre-mix flux and the flux ofperipheral complementary air is ejected in a convergent flow and instrong spiral rotation.

To this effect the burner is configured in the example with acone-shaped deflector 18 at the exit of the central pipe 13 and blades19 in the pipe which put the central flux of air into rotation. Otherequivalent means may also be suitable, as for example calibrateddirectional orifices or oriented ports in a separating partition.

Preferably the central air is divergent with an angle at the top of 60to 180° or of 30 to 90° in relation to the axis of the burner.

This ejection produced in this way allows achieving good penetration ofthe air in the pre-mixture so as to best complete the rate of missingair.

The flux of central air of the example has previously penetrated theintake 9 in the internal conduit of pipe 13, in the ring space aroundthe central pole 51.

If applicable, this central air can have another function that isexplained later on, which is to feed at its ejection base a rich gaswhich would be distributed in ring shape around the central air, duringits use, in particular during startups or shortages of lean gas.

As to the peripheral complementary air, the burner is configured withinjection nozzles 20 a, 20 b located on a ring 14 on the front end orface of chamber 26 a. The nozzles are oriented both tangentially to acircle centered on the central axis and oriented towards the front.Spiral rotation is obtained by this dual slant of the nozzles.

The peripheral air wraps around the flux of lean gas and enhances itsrotation. It is distributed at high speed and optimizes the mixing.

Nozzles 20 a, 20 b are fed by the space of peripheral pre-ejection 30located in a double partition of the chamber at the front of the chamberwhich is itself fed by the intake devices 10A that have been provided inthe vicinity of the back end 26 b of the chamber.

The sub-components of the burner are now described below, with referenceto the corresponding figures, namely, the chamber, the central tube andthe central pole.

The chamber of the burner:

In reference to FIGS. 6 to 9, the chamber 7 has a general rotationalshape and consists of:

-   -   a dual peripheral wall formed by an external wall 24 and an        internal one 25,    -   a front end or face 26 a, formed by a ring 14 including the        means for peripheral injection 20 a, 20 b;    -   a back end or face 7B including different intakes or feeds 10,        10A at least for a flux of peripheral air and of pre-mixture,    -   a space 27 for air circulation divided by the double wall        allowing to let the two ends 26 a and 26 b be in communication        with each other,    -   intake ports 8 on the double peripheral wall, these ports being        intended to interface each other between an internal space 16 in        the so-called pre-mix space chamber and the outside,    -   conduits, in the form of hollow girders 11, located in the        thickness of the double wall, these conduits extending between        the ports 8, between a receiving space for air flux 10A or        intake located at the back end 7B and a pre-ejection space 30 of        the peripheral air located at the front end, and    -   pre-mix air injection nozzles 17 located under the conduits,        these nozzles being configured so as to perform said first        permanent injection of pre-mix air, these conduits and the        nozzles being part of the means of incorporation mentioned        previously.

The nozzles are in fact exit perforations made in the ring one of thefunctions of which is to close off the front end of the double wall ofthe chamber. The other back end of the double wall is closed off by awall 23B.

These perforations communicate with the pre-ejection space 30 of thedouble wall and lead to the outside through an internal wall of thechamber. The nozzles are arranged on the ring, being offset relative tothe radial axis R of the chamber and slanted towards the front relativeto a plane perpendicular to the chamber.

The nozzles are offset and slanted in different ways according to analternation. The angles proposed are specific to this power of theburner, but would be inevitably modified for another size burner. Theseangles have been determined so that the jets of consecutive orifices donot interfere with each other and do not collide with the end of tube 13nor impede the flow of fluids coming out of the gas ring containedbetween 13 and 56, nor the divergent complementary central air. Thisdivergent cone must practically “mesh” with the convergent complementaryperipheral jet with the most acute angle (here 15°).

The angle of the next orifice is more open in order to continue furtheralong in the rotation the work of the preceding orifice.

A first series of nozzles (20 a) maybe slanted from 5° to 45° to thefront, (15° preferred in the example of execution) and from 30 to 65°relative to the radial axis (R), (44° preferred in the example) and asecond series of nozzles (20 b) slanted from 25 to 65° to the front (45°preferred in the example), and from 30 to 70° relative to the radialaxis (53° preferred in the example).

The chamber may also include orifices 55 arranged on the internal wall25 at the height of the pre-ejection chamber 30. These orifices permitfeeding the blade device 37 from the chamber 30 in order to improve theair/lean gas mixture between the blades.

The central tube:

In reference to FIGS. 10 and 11, a central tube 13, meant to beinstalled centered on the central axis, is dimensioned to extendlongitudinally between the two ends of the chamber and to put incommunication with each other.

This tube includes:

-   -   an outside surface 35 for the purpose of delimiting the pre-mix        space with the inside wall 25 or the inside face 31 of the        double wall of the chamber, and an inside surface 52;    -   fasteners at the chamber and reception devices of an air or gas        chamber located at the end of the tube; and    -   a first set of blades 37, located at the front of the tube, said        blades 37 extending into the pre-mix flow space between the        outside wall 35 of the tube and the inside wall of vessel 25 or        inside face 31.

The blades are profiled so as to create a rotation of the pre-mix fluxduring its flow towards the exit of the vessel. A space between thevessel and the tube forms a ring-shaped conduit 38 (FIG. 1) intended toconvey the flux of pre-mix air. A wall 23 forms a radial collar of thecentral tube, said wall separating the pre-mix space with the back endof the central tube which is itself in communication with the airchamber.

The central pole:

In reference to FIG. 12, the central pole 51 is intended to be locatedin the central tube 13 and centered on the central axis.

The burner also includes a second set of blades 19 located inside and inproximity to the front end of the central tube.

In the example, the blades are attached to the central pole 51 whichcrosses the central tube. They are meant to extend from the surface ofthe pole 50 to the inside wall 52 of the central tube.

The burner may also include a “burn cone” 18 as a deflector locateddownstream of the central tube and spaced from it so as to provide adivergent outflow of the central flux of air. In the example shown, theburn cone is placed at the front end of the axial pole 51.

The gas is ejected at the end of the pole, at a divergent angle that isdefined by a series of calibrated orifices 54 placed in a ring formaround the cone shaped deflector 18 which allows to eject this gas overa maximum circumference so that any rich gas jets that may be presentand originate as close as possible to the central combustion air andhave maximum momentum when colliding with the flow of lean gas.

Preferably, for best results, the cone shaped deflector maybe adeflector 18 b with a peripheral serration 52 and have central orifices53 leading to the inside of the conduit of the central pole.

In general, the burner is designed to receive, under normal operatingconditions, an ejection of complementary flux at a very high speed above100 m/second whereas the pre-mix flux is ejected at a speed between 40and 80 m/sec.

If applicable in a variant of execution, the burner may include a richgas supply. In the example, the rich gas is brought in under pressure tothe periphery of the central tube directly to the pre-mix space.

Preferably, for very high capacity burners (over 20 Megawatt), the richgas is distributed around the central tube so as to mix thoroughly withthe pre-mixture.

To that effect the central tube may contain:

-   -   a ring-shaped vessel 36 for receiving and distributing gas        around several orifices crossing the rear wall 23 in the shape        of a radial collar of the central tube;    -   a portion of tube 56 arranged in double wall around the central        tube so as to convey the flux entering the pre-mix chamber to        essentially half way into the chamber; and    -   a connection cone 57 from the double wall to the vessel through        the intermediary of the collar so as to collect the rich gas;    -   as an accessory, a ring-shaped deflector 58 placed at a distance        from the end of the double wall so as to diverge the rich gas        and promote a good stirring with the air; and    -   alternatively or as a complement to the deflector above, a        series of orifices 59 that are calibrated and placed across the        central tube is arranged in form of a ring just upstream of the        deflector 58 so as to let the complementary central air be        ejected into the flux of rich gas and to contribute in this way        to make it diverge.

According to a variant of execution, the vessel 36 maybe connected to arich gas supply tube (the orifices 10A2 being blanked off) or anothervessel 36B (not shown) wrapped around vessel 36 and connected to thesupply tube. Calibrated orifices arranged with a divergent angle may bemade in a ring connecting the two tubes 13 and 56B at the front end.

Possibly, the double wall 56 tube portion may extend to the end of thecentral tube 13, forming a central double wall 56B so as to eject therich gas directly to the gas port nose around the central air.

On the other hand, for burners of lower capacity (for instance less than20 MW), the rich gas is, still under pressure, brought into the centralpole. It is ejected at a defined divergent angle by a series ofcalibrated orifices 53 arranged in a ring around a particular device(deflector with peripheral serration 52) which allows to eject this gason a maximum circumference so that the rich gas jets originate as closeas possible to the combustion air and have maximum momentum whencolliding with the flow of lean gas.

The above configurations make it possible to obtain a consistent flameof a continuous structure and maximum surface (optimization of thermaltransfer in the burn chamber). The rich gas is thus supplied withcombustion air at its base, whatever the composition/proportion of thefuels: single and pure gas or gas in mixtures.

The burner is designed in mechanic/welded modules which allow for amaximum of flexibility and ease of design, adaptation, construction,installation and maintenance, in the knowledge that:

-   -   the combustion air may be more or less hot,    -   for installations with multiple burners mounted next to each        other, the directions of rotation of the fluids must be        coordinated so they won't upset the combustion and the flows in        the burn chamber,    -   it allows to easily replace existing burners, and    -   the rich fuels may be of different qualities.

The possible flows of the different flux are described in accordancewith one operating mode of the burner.

An ignition flame is brought to the nose of the burner through theintermediary of a guide tube 60 (FIG. 1). The permanent air system isthen activated by a pump (not shown) which blows combustion air into theback end of the burner by putting the air supply vessel ZC underpressure.

A fraction of the combustion air penetrates into the double wall 27 ofthe vessel (FIG. 6) across the inlet orifices 10 that are for examplerectangular and made in the ring-shaped wall 23B closing the double wallat the rear. Whereas another fraction penetrates directly into thedouble vessel towards the nozzles 20 a, 20 b.

A portion of this fraction penetrates into the girders 11 (FIG. 8),whereas the other portion feeds directly into a pre-ejection chamber ofperipheral air 30 by way of a partial, so-called deflection double wallof the vessel (FIG. 7) which features no ports and which extends at anangle of approximately 90° between the radial walls 32 and 33.

The girders are put under pressure and combustion air escapes from thenozzles in a tangential direction (FIG. 7) to a circle centered on thecentral axis and towards the blades of the first rotation device.

The combustion gas which may be under light pressure (generally lessthan 200 CE) enters crosswise into the vessel under an effect ofentrainment of the air jets at the level of the ports 8 between thegirders 11. The turbulence results in a pre-mixing or stirring insidethe pre-mix space 16 of the vessel at the entry of the blade device(FIG. 7), especially by deflection against the deflection wall 31.

Since the girders also open into the pre-ejection chamber 30 ofperipheral air, they contribute to the air supply there in addition tothe air conveyed by the inside of the deflection or guide double wall24, 25.

Combustion air also penetrates by entry 9 of the central tube 13 (FIGS.10, 11) and opens directly at the level of the nose 6, after havingentered the space between the blades of the second blade device 19 (FIG.2) where it assumes a rotational movement. This air re-exits in front ofthe nose in a deflecting manner by way of the cone shaped deflector 18placed in front of it.

During this time the peripheral air is ejected from the chamber 30(FIGS. 9, 14-16) in the form of two swirls by way off the peripheralnozzles 20 a, 20 b in front of the gas port nose.

When the pre-mixture arrives at the exit in front of the burner where itis ejected in a ring shaped swirl, it is squeezed and stirred betweenthe central and peripheral flux of air which penetrate it thoroughly.

The rotational direction of the different flux of air may be oppositethat of the pre-mix flux, but preferably they should be in the samedirection.

If applicable, supplemental air may enter the pre-mixture chamber bytubes 21 or flaps (FIGS. 10, 11) arranged on a ring-shaped wall 23coming from the collar of the central tube and helping to enrich the airmixture.

Air may also come from the back end of the vessel 36 through orifices10A2 and enrich the pre-mixture.

If applicable (FIG. 6), air may escape from the vessel beginning fromthe pre-ejection chamber 30 through orifices 55 made in the inside wallof the vessel and it penetrates radially in the blade device 37 betweenthe blades. This helps to improve the stirring of the gas mixture withair.

If several burners are used which are arranged near each other in acombustion chamber of an installation, care must be taken to ensure thatthe different swirls mesh. To this effect, the orientation of differentnozzles and blades must be adapted. For example, the peripheral swirlsshould be working in opposite between two burners.

In this way the invention provides the following advantages:

-   -   the flame is stable and has caught on well, and one eliminates        all the vibrations caused by unstable combustion;    -   no adjustment is required;    -   the combustion air can be divided into more than two, even more        than three fractions;    -   there is no need for a support fuel to compensate for        irregularities in the mixture or in the leanness of the fuel        gas, nor for devices or associated equipment which allows you to        save rich gas if there is a shortage of lean gas;    -   possibility to function normally with pure rich gas and rich gas        only;    -   elimination of the need for heating gas or combustion air, as a        result of the burner's capability to properly burn gases with        very low NCV (<750 Kcal/m³) in cold gas and cold air; generally        heating of combustion air of a 20 MW occurred at 200° C. [392°        F.];    -   reduction in the oxygen content of fumes because of very good        combustion due to an optimized air-fuel mixture. The oxygen        content in fumes has been reduced to 0.6-1% instead of 2%;    -   there is a rise in the flame temperature from 60 to 80° C. [140        to 176° F.] bringing about a significant increase of thermal        transfers in the combustion chambers (+15%), productivity of the        boiler being thereby improved, if the re-superheating can        follow;    -   there is a significant reduction of losses to fumes (at constant        temperature) because the volume of fumes drops in the same        proportion as the air factor, by 10 to 15%, thereby the boiler        output being improved by at least 1 point, for a 100 MW boiler,        representing more than 10 GWh/year of fuel; and    -   reduction of electric power consumption of ventilators for air        and fumes to be stirred to the extent that the volumes of air        and fumes to be stirred are smaller, this also resulting in        smaller size (by 15 to 20%) blower and draught fans and a        reduction in their power consumption of more than 10%.

1. Method to achieve combustion of lean fuel gas using at least oneburner comprising a combustion nose on a central axis, said methodcomprising the steps of: creating a pre-mixture containing pre-mixtureair and fuel gas, said pre-mixture being inflammable; and ejecting, infront of said combustion nose, said pre-mixture in a flux of pre-mixturein rotation around said central axis and a complementary flux, anignitibility threshold of the mixture in front of the gas port nosebeing reached, a flux being ejected in a center of the pre-mixture fluxby way of a central complementary flux or around the pre-mixture flux byway of a peripheral complementary flux.
 2. Method as per claim 1,wherein said complementary flux is comprised of a flux of air.
 3. Methodas per claim 1, wherein the pre-mixture flux is obtained byincorporation of pre-mixture air into fuel gas.
 4. Method as per claim3, wherein said incorporation is carried out in a vessel connected tothe burner.
 5. Method as per claim 3, wherein said incorporation isperformed, at an entry of the fuel gas in the burner, by an injection ofpre-mix air so that this injection of pre-mix air drives that fuel gasinto a pre-mixture space and achieves the pre-mixture by turbulenceresulting from the injection and directs the pre-mixture towards thecombustion nose while initiating a rotation around the central axis. 6.Method as per claim 1, wherein the complementary flux is ejected inrotation in the same sense of rotation as the pre-mixture flux. 7.Method as per claim 1, wherein the flux of central complementary air isejected in rotation in front of the gas port nose or head and indivergent flow in order to penetrate the flux of pre-mixture, andwherein the flux of peripheral complementary air is ejected inconvergent flow and in strong spiraled rotation.
 8. Method as per claim1, wherein the mixture of fuel gas and combustion air is achieved byincorporating a necessary partitioned quantity of one in the other bynumerous oriented jets.
 9. Burner for lean fuel gas, the burnercomprising: a gas port nose on a central axis; and a means for creatinga non flammable pre-mixture containing a pre-mixture air and fuel gasthe pre-mixture being ejected in front of the combustion nose, thenon-flammable pre-mixture being in a flux of pre-mixture in rotationaround the central axis, the pre-mixture in front of the combustion nosehaving a complementary flux so as to reach an ignitability threshold, aflux of the mixture being ejected at a center of the pre-mixture flux byway of a central complementary air flux or around the pre-mixture fluxby way of a peripheral complementary air flux.
 10. Burner as per claim9, wherein an air flux is comprised of at least one flux of pre-mixtureair; and one flux of complementary air, said one flux of complementaryair being comprised at least one flux of central complementary air orone flux of peripheral complementary air.
 11. Burner as per claim 9,wherein the complementary flux is ejected in rotation in the same senseof rotation as the pre-mixture flux.
 12. Burner as per claim 9, whereinthe flux of central complementary air in rotation in front of thecombustion nose and in divergent flow to penetrate the pre-mixture flux,and the flux of peripheral complementary air in convergent flow and instrong spiraled rotation are ejected.
 13. Burner as per claim 9, furthercomprising: means for incorporating pre-mixture air into fuel gas,obtaining the pre-mixture flux.
 14. Burner as per claim 13, said meansfor incorporating comprising: means for injecting a first permanentinjection of pre-mixture air into a pre-mixing upstream of the gas portnose, said space being intended to be in communication with an enclosurecontaining the fuel gas, said injection being performed so as to drivethe fuel gas into the pre-mixture space, to achieve the pre-mixture byturbulence resulting from the injection and to direct the pre-mixturetowards the gas port nose while initiating a rotation around the centralaxis.
 15. Burner as per claim 14, said means for incorporating furthercomprising: a second means for injecting pre-mixture air, said secondmeans for injecting being arranged so as to achieve an incorporation ofair parallel to the central axis in a progressive manner, depending onthe level of power used, and so as to direct the pre-mixture flowtowards the gas port nose.
 16. Burner as per claim 9, furthercomprising: a cylindrical vessel having a peripheral double wall, afront end configured to deliver the flux of peripheral air on the gasport nose, and a back end configured to receive at least air flows, thetwo ends communicating with each other by way of an air circulationspace divided by the double wall, said cylindrical vessel havingentrance ports on the peripheral double wall intended to interface eachother between an internal, so-called pre-mix space space in the vesseland the outside in a gas-holding enclosure, and said cylindrical vesselhaving conduits, being comprised of hollow girders, located in thethickness of the double wall and extending between the ports between areceiving space of air flux situated at the back end and a pre-ejectionspace of peripheral air situated at the front end, said conduitscomprising pre-mix air injection nozzles configured so as to achievesaid first permanent injection of pre-mixture air.
 17. Burner as claim16, further comprising: a central tube centered on the central axisinside the cylindrical vessel and extending between the two ends of thevessel (26 a, 26 b) said tube being comprised of an outside surfaceintended to define the pre-mixture space with the internal wall of thedouble wall of the vessel, fasteners at the vessel and reception devicesof an air or gas chamber (36) located at the end of the tube, and afirst set of blades 37, located at the front of the tube said bladesbeing profiled so as to create a rotation of the pre-mix flux during itsflow towards the exit of the vessel and extending in the pre-mix flowspace between the outside wall of the tube (35) and the inside wall (31)of the vessel.
 18. Burner as per claim 17, said tube being furthercomprised of a second blade device located inside and in the vicinity ofthe front end of the central tube, said blades being attached to acentral pole and extending between the surface of the pole and theinside wall of the central tube.
 19. Burner as per claim 15, wherein thesecond air injection is performed through the intermediary of orificeslocated on a wall in the form of a collar of the central tube, said wallseparating the pre-mixture space with the back of the central tube incommunication with the air vessel, said orifices being closed off byflaps that can be operated by scaled springs or by switchable controls.20. Burner as per claim 16, said cylindrical vessel further comprisingexit perforations in the form of nozzles communicating with thepre-ejection space in the double wall and discharging to the outside onan internal wall of the vessel or equivalent, said nozzles beingarranged in ring form and offset relative to the radial axis of thevessel and being directed towards the front.
 21. Burner as per claim 20,further comprising: a first series of nozzles slanted forward between 5°and 45° and between 30 and 65° relative to the radial axis and a secondseries of nozzles slanted forward between 25° and 65° and between 30°and 70° relative to the radial axis.
 22. Burner as per claim 18, furthercomprising: a burn cone forming a cone-shaped deflector locateddownstream of the central tube and spaced from the central tube so as toprovide a divergent outflow of the central flux of air.
 23. Burner asper claim 22, wherein the cone-shaped deflector is located at the end ofthe axial pole crossing the central tube.
 24. Burner as per claim 22,wherein the cone-shaped deflector is comprised of a peripheral serrationand central orifices leading to the inside of the conduit of the centralpole.
 25. Installation for the combustion of a fuel gas, implementingthe method as per claim
 1. 26. Installation as per claim 25, furthercomprising the step of using at least two burners so configured as tomesh in the same direction the overall rotational movement resultingfrom their mixture flow in front of the gas port nose.